Bonin Flying Fox (Pteropus pselaphon)

The Bonin flying fox (Pteropus pselaphon) is a medium‑sized megabat belonging to the family Pteropodidae. Endemic to the Ogasawara (Bonin) Islands of southern Japan, it occupies only three small islands—Chichijima, Hahajima, and Anijima—where it roosts in coastal forests and mangrove thickets. Adults have a wingspan of roughly 900–1,000 mm and a head‑body length of 210–260 mm, with a soft, dark‑brown pelage and a distinctive pale‑yellowish throat patch. Unlike many mainland flying foxes, the Bonin species lacks a pronounced facial mask and has relatively short forearms, adaptations thought to aid maneuvering among the dense island vegetation. The species is nocturnal, emerging at dusk to feed on native fruits, figs, and nectar from flowering trees such as Ficus and Metrosideros. Because its range is restricted to less than 100 km² of forested habitat, the Bonin flying fox is highly vulnerable to habitat loss, invasive predators, and stochastic events. The IUCN Red List classifies it as Endangered, with an estimated population of 500–800 mature individuals. Conservation actions focus on habitat protection, invasive species control, and community‑based monitoring to prevent further declines.

Bonin flying foxes are social mammals that form colonies ranging from a few dozen to several hundred individuals, typically roosting in the canopy of native evergreen trees or in abandoned caves near the coast. Colonies are mixed‑sex but display a loose hierarchy in which older males defend temporary perches and females maintain close proximity to their offspring. The species is primarily nocturnal; individuals leave the roost at twilight and travel up to 5 km to forage, often following established fruiting corridors. Vocal communication includes low‑frequency squeaks and bark‑like calls used for group cohesion and predator alerts. Grooming is frequent and serves both hygienic and social bonding functions. Home ranges overlap considerably among neighboring colonies, but each female tends to reuse a core foraging area that overlaps with the territories of several males, facilitating a promiscuous mating system. Seasonal fluctuations in fruit availability drive temporary shifts in colony size, with larger aggregations observed during peak fruiting periods of native figs.

The Bonin flying fox is primarily frugivorous, relying on a diet of native and introduced fruits, figs (Ficus spp.), and the nectar of flowering trees such as Metrosideros polymorpha and Pandanus spp. Individuals consume up to 150 g of fruit per night, selecting ripe, sugar‑rich portions that provide the high energy needed for sustained flight. In addition to fruit pulp, they ingest seeds, which are later dispersed across the islands, playing a crucial role in forest regeneration. Nectar feeding involves hovering at flower clusters and using a long tongue to lap up nectar, supplementing their carbohydrate intake during periods of fruit scarcity. Occasional ingestion of pollen and insects has been recorded, but these constitute less than 5 % of the diet. Foraging bouts typically last 30–45 minutes, after which bats return to roost sites to digest and excrete seeds. Seasonal shifts in fruiting phenology cause the bats to adjust their diet composition, increasing reliance on nectar during the lean winter months of December to February.

Females of Pteropus pselaphon reach sexual maturity at about 12 months, while males mature slightly later at 14–16 months. Breeding is timed to the island’s seasonal fruiting cycle, with most conceptions occurring between March and May, when food resources are abundant. The gestation period lasts approximately 180 days, after which a single pup is born, weighing around 30 g. Newborns are altricial, blind and hairless, and cling to the mother’s nipple for the first two weeks. Lactation continues for 4–5 months, during which the mother forages nightly and returns to the roost to nurse. Pups are weaned at about 6 months and become volant shortly thereafter, remaining within the maternal colony for several months before dispersing to establish their own foraging routes. Longevity of reproductive females can exceed 10 years, allowing for multiple breeding cycles over a lifetime, though reproductive success is highly variable and closely linked to annual fruit production.

The IUCN Red List classifies the Bonin flying fox as Endangered, with an estimated 500–800 mature individuals confined to three small islands. The principal threats are habitat loss due to agricultural expansion, urban development, and the replacement of native forest with monoculture plantations, which reduces the availability of key fruiting trees. Invasive species, particularly the black rat (Rattus rattus) and feral cats (Felis catus), prey on pups and compete for food resources, contributing to low recruitment rates. Cyclones and typhoons pose stochastic risks, capable of destroying roost trees and causing mass mortality. Climate change may alter fruiting phenology, further stressing food availability. Conservation measures include the designation of protected areas on Chichijima and Hahajima, eradication programs targeting invasive mammals, and community outreach to promote the ecological importance of seed dispersal by the bats. Ongoing population monitoring indicates a slight decline over the past decade, underscoring the urgency of sustained management actions.

• The Bonin flying fox is one of the smallest members of the genus Pteropus, with a wingspan under 1 meter.
• It plays a keystone role in seed dispersal for many endemic island plant species.
• Unlike many bats, it lacks a pronounced facial mask, giving it a relatively plain appearance.
• The species can travel up to 5 km from its roost to forage, despite its limited island range.
• Conservation efforts have successfully eradicated rats from several key roost islands, improving pup survival.